The hemodynamic response of the conscious pregnant guinea pig to nicotine.

The hemodynamic response to continuous intravenous infusion of nicotine, at 4.5 and 18 micrograms/min, was measured using radiolabeled microspheres in nine chronically catheterized pregnant guinea pigs. These gave serum nicotine levels of 72.3 +/- 6.6 ng/ml and 315 +/- 32 ng/ml (mean +/- SEM), respectively. During low-dose nicotine infusion there was no significant change in cardiac output, its distribution, or uteroplacental blood flow. During high-dose nicotine infusion, cardiac output fell from 257.8 +/- 30.9 ml/min to 212.7 +/- 19.3 ml/min (p less than 0.05) and uteroplacental blood flow fell from 31.2 +/- 3.1 ml/min to 22.3 +/- 2.4 ml/min (p less than 0.05). During control, low-dose, and high-dose periods, serum epinephrine levels rose from control value of 60.2 +/- 2.6 to 98.9 +/- 35 and 1200 +/- 295 pg/ml (p less than 0.05 low dose versus high dose) and serum norepinephrine levels did not change significantly during nicotine infusion. Hence at nicotine levels 20 times but not at two to five times those seen in smokers, modest reductions in cardiac output and uteroplacental blood flow were observed.